The present invention relates generally to electronic devices such as portable radiotelephones. More particularly, the present invention is directed to operating a communication device to reduce current drain.
In a battery-operated device, such as a portable communication device, methods can be utilized to put the device in a low power mode and reduce current drain so that the battery charge lasts longer. In a wideband code division multiple access (W-CDMA) cellular communication system, one technique involves entering a low power or xe2x80x9csleepxe2x80x9d mode where much of the hardware is shutdown and the high-speed clock is turned off. The clock source requires significant power to operate, and circuits consume more current as the driving clock speed increases. Many microprocessor-based products other than WCDMA devices have similar states they enter where certain hardware portions and clocks are powered off and must be powered on and become stable before the system can operate again. For example, wireless local area networks, such as Bluetooth(trademark) processors can turn off portions of themselves in accordance with low power mode instructions. In regards to communication functions, an idle mode can be defined for a battery-operated mobile radio, such as a cellular radiotelephone. In this mode, when the radiotelephone is in the idle mode (i.e., not engaged in a call), the radiotelephone does not continuously monitor a control channel but generally remains in a low power, idle state. In the idle state, the radiotelephone wakes up only during predetermined time slots to see if there is an incoming call, as indicated on a control or pagiong channel, or to process some other condition, such as a user input. The goal of low power or idle mode operation is to reduce the on time of the radio to a minimum arid to power down as much of the radio as possible during sleep periods, thereby preserving battery life.
A cellular phone is typically in an operating mode where it must periodically wake-up from deep sleep to monitor information or perform some other physical layer (layer 1) event. In addition, there are procedures followed to get into sleep mode and a procedure to get out of sleep mode. The procedures involve some delay when entering or exiting sleep mode primarily to allow the hardware to warm-up and the clock source to become stable. During these delay times, and in addition to the wake-up periods, the current drain of the phone is increased over that during a sleep mode. Therefore, not only is it desireable to reduce total on-time for the clock, it is desirable to avoid entering and exiting deep sleep and experiencing the associated additional high current drain delay times.
Today""s communication devices can not only include wide area network connectivity, such as over WCDMA, but can also include wireless local area networking (WLAN). This usually involves coupling a separate processor or even a complete device, dedicated to WLAN connectivity, to an existing communication device. One result of this coupling is that the cellular processor and WLAN processor can share much of the hardware of the device, including the user interface, battery, and the clock oscillator in particular. The clock oscillator can then supply a clock signal to both processors. Either of the processors can direct the clock to wake-up from a sleep mode for a layer 1 activity for the cellular communication or for local activity. These activities are not synchronized to each other. Therefore, the clock must wake up independently to perform any particular communication at the required time. As a result, the clock oscillator enters and exits sleep mode many times, asynchronously from those times required to enter and exit sleep mode for the cellular layer 1 communication activities.
Accordingly, there is a need for a method for controlling clock sleep modes in a communication device operable in two communication systems. There is a further need to reduce the frequency of entering and exiting sleep modes, and to remain in sleep mode as long as possible.